This application is based on and incorporates herein by reference Japanese Patent Application Nos. 2000-105276 filed on Apr. 6, 2000, 2000-189600 filed on Jun. 23, 2000, and 2000-337838 filed on Nov. 6, 2000.
1. Field of the Invention
The present invention relates to a pressure reducer in a refrigeration cycle unit suitable for use in a vehicle air-conditioner.
2. Description of Related Art
A temperature type pressure reducer has been normally used as a pressure reducer to automatically control the flow rate of refrigerant so that the degree of superheat of refrigerant at the output of an evaporator is maintained at a predetermined value because the width of fluctuations of cycle operating condition is large in a vehicular air-conditioning refrigeration cycle unit. However, the structure of the temperature pressure reducer is complicated and is expensive because it requires a valve driving mechanism which operates corresponding to the degree of superheat of the refrigerant at the output of the evaporator.
Then, there has been proposed a pressure reducer having a simple structure by eliminating the valve driving mechanism in JP-A-11-257802. In this prior art, a pressure reducer having a valve mechanism for changing a restrict diameter corresponding to differential pressure (difference between high pressure and low pressure of the cycle) before and after the pressure reducer is constructed as shown in FIG. 22 in a refrigeration cycle unit. In the accumulator type refrigeration cycle unit, an accumulator for collecting liquid refrigerant by separating gas and liquid of the refrigerant is disposed between the outlet of the evaporator and the suction side of the compressor.
According to the prior art, the valve mechanism expands the restrict diameter when the circulating flow rate of the cycling refrigerant is balanced with the radiating capability of the condenser and the differential pressure is smaller than a first predetermined value P1 in running normally for example. Then, the valve mechanism reduces the restrict diameter when the radiating capability of the condenser drops due to the reduction of the cooling air amount and the high pressure increases, thus increasing the differential pressure more than the first predetermined value P1 in idling. Then, the valve mechanism expands the restrict diameter again when the flow rate of the cycling refrigerant rises remarkably due to the high-speed rotation of the compressor in running at high-speed for example and the high pressure rises further, thereby increasing the differential pressure more than a second predetermined value P2.
Thus, the valve mechanism lowers the low pressure by reducing the restrict diameter in idling to assure the cooling capability in idling and expands the restrict diameter in running at high-speed to prevent the high pressure from rising abnormally in the prior art.
However, the actual relationship between the refrigeration cycle operating condition and the differential pressure (difference of high pressure and low pressure in the cycle) before and after the pressure reducer is not determined uniquely as shown in FIG. 22. For instance, there is a case when the high pressure rises and the differential pressure becomes greater than the second predetermined value P2 when the radiating capability of the condenser drops extremely even in idling when the outside temperature is high or when the traffic jam occurs in a city and the valve mechanism expands the restrict diameter similarly to the case of running at high-speed. As a result, there arise problems that the low pressure (refrigerant evaporating temperature) rises and the subcooling degree of the refrigerant at the outlet of the condenser reduces, thereby dropping the cooling capability.
A vehicular transmission gear is shifted to low-speed gear and the flow rate of the cycling refrigerant rises remarkably due to the high-speed rotation of the compressor in running an uphill road even in running normally. However, since the car speed is low in running the uphill road, it is often unable to obtain the cooling air amount of the condenser corresponding to the rise of the flow rate of the refrigerant. As a result, there is a case when the high pressure rises and the differential pressure becomes greater than the first predetermined value P1 as the radiating capability of the condenser becomes insufficient. The valve mechanism reduces the restrict diameter similarly to the case in idling at this time. Thereby, the high pressure rises further, thereby increasing the driving power of the compressor and worsening the efficiency of the cycle.
In view of the problems described above, an object of the present invention is to provide a pressure reducer having the small and simple structure and capable of controlling the flow rate of refrigerant favorably even when the operating condition fluctuates widely.
In the accumulator type refrigeration cycle unit in which an accumulator for collecting liquid refrigerant by separating the gas and liquid of the refrigerant is disposed between the outlet of the condenser and the intake side of the compressor as disclosed in JP-A-11-257802, saturated gas refrigerant is taken in from the accumulator and is compressed and discharged. Then, the condition (subcooling degree or dryness) of the refrigerant at the outlet of the condenser changes due to the fluctuations of the cycle operating condition. It is effective to maintain the subcooling degree of the refrigerant at the outlet of the condenser in an adequate range (around 7-15xc2x0 C.) in order to improve the efficiency of the refrigeration cycle.
That is, when the subcooling degree of the refrigerant at the outlet of the condenser becomes excessively large, the driving power of the compressor increases due to the rise of the high pressure. When the subcooling degree of the refrigerant at the outlet of the condenser becomes excessively small in contrary, the difference of enthalpy between the inlet and outlet of the evaporator decreases, thus dropping the capability.
Then, the present invention achieves the above-mentioned object by favorably controlling the flow rate of refrigerant with respect to the wide fluctuations of the driving condition while maintaining the subcooling degree of the refrigerant at the outlet of the condenser in the appropriate range.
According to a first aspect of the present invention, variable restrict means is disposed at the upstream side of flow of the refrigerant. Fixed restrict means is disposed at the downstream side of the variable restrict means, and refrigerant which has passed through the variable restrict means always flows thereto. An intermediate space is provided between said variable restrict means and the fixed restrict means, and passage sectional area of which is larger than that of the fixed restrict means. The length of the intermediate space is larger than a predetermined length required for allowing the refrigerant injected out of the variable restrict means to expand more than a passage sectional area of the fixed restrict means.
The fixed restrict means has the shape of a nozzle or the like. The change of flow rate is large, i.e., a flow rate control gain is large, in the area B where the dryness of refrigerant is small (dryness x less than 0.1 for example) as indicated by a dot chain line (1) in FIG. 3 described later.
Then, noticing on this point, the variable restrict means disposed at the upstream side of the flow of refrigerant decompresses the subcool liquid refrigerant at the outlet of the condenser by a predetermined degree to change to the small dryness area, the gas-liquid two phase refrigerant in the small dryness area is flown into the fixed restrict means to decompress again.
Thereby, the refrigerant flow rate control action can be performed in the refrigerant state in which the flow rate control gain is large by the fixed restrict means, so that a large refrigerant flow rate control width D (FIG. 5) can be obtained by a small variation width C of the subcooling degree as indicated by (2) in FIGS. 3 and 5 when the flow rate control action of the fixed restrict means is seen from the relationship with the subcooling degree of the refrigerant at the outlet of the condenser.
Specifically, because the restrict means at the upstream side of the flow of refrigerant is the variable restrict means whose throttle opening can be controlled, an adequate dryness state may be created by the flow rate control action of the fixed restrict means at the downstream side by controlling the throttle opening of the variable restrict means corresponding to the changes of state of the refrigerant at the outlet of the condenser.
Further, the part of the flow of refrigerant where the flow velocity is high and the part thereof where the flow velocity is low may be mixed in the intermediate space by injecting the refrigerant in the small dryness area decompressed by the variable restrict means to the intermediate space where the passage sectional area is larger than that of the fixed restrict means and by expanding the flow of injected refrigerant more than the passage sectional area of the fixed restrict means within the intermediate space. Therefore, the injected flow of refrigerant from the variable restrict means (14) can be a flow of relatively uniform flow velocity and this uniform flow of refrigerant may be restricted steadily according to the flow rate characteristic of the fixed restrict means at the downstream side. The flow rate characteristics indicated by (1) in FIG. 3 may be exhibited steadily by the restricting action of the fixed restrict means.
As a result, the refrigerant flow rate may be controlled in the wide range by the small variation width of the subcooling degree of the refrigerant at the outlet of the condenser even when the refrigeration cycle operating condition fluctuates widely. Therefore, the subcooling degree of the refrigerant at the outlet of the condenser may be kept in an adequately range for improving the efficiency of the cyclic operation, thereby achieving the highly efficient cyclic operation and the assurance of the cooling performance. Further, because it requires no valve driving mechanism which corresponds to the degree of superheat such as temperature type pressure reducer and the small and simple pressure reducer comprising the variable restrict means and the fixed restrict means may be constructed.
According to a second aspect of the present invention the pressure reducer includes bleeding means for allowing the intermediate space to communicate with an upstream side passage of the variable restrict means even when the variable restrict means is closed.
It allows the refrigerant to be flown through the bleeding means even when the variable restrict means is closed, so that it is possible to prevent the variable restrict means from hunting when the flow rate is small while closing the variable restrict means until when the refrigerant flow rate increases to a predetermined flow rate.
According to a third aspect of the present invention, the variable restrict means has a fixed valve seat and a valve body displacing with respect to the fixed valve seat. The valve body displaces in accordance with a pressure difference between at an upstream side and a downstream side thereof.
Thereby, it is possible to keep the pressure difference at a constant value regardless of the fluctuations of the operating condition and to maintain the flow rate control action of the fixed restrict means at the downstream side in a favorable state at all times by changing the subcool liquid refrigerant at the outlet of the condenser to the small dryness area by the variable restrict means.
According to a fourth aspect of the present invention, the pressure reducer includes spring means for urging the valve body toward a valve closing direction against the pressure difference, and the spring force of the spring means is adjustable.
Thereby, the pressure difference may be controlled by setting the spring force of the spring means and the target subcooling degree of the refrigerant at the outlet of the condenser may be readily controlled by controlling the pressure difference. Accordingly, the target subcooling degree may be controlled readily by controlling the spring force of the spring means even when heat exchanging capability is difference due to the change of size of the condenser and the evaporator and when the heat radiating condition of the condenser is changed.
According to a fifth aspect of the present invention, the pressure reducer includes a body member for containing the variable restrict means. The fixed valve seat is assembled to the body member so that its position can be adjusted and the spring force of the spring means is adjusted by adjusting the position of the fixed valve seat.
Thereby, the target subcooling degree may be adjusted readily by adjusting the position of the fixed valve seat with respect to the body member.
According to a sixth aspect of the present invention, the pressure the spring force of the spring means is preset at 3-5 kg/cm2.
According to the experiments and study conducted by the inventors, it was found that the subcooling degree of the refrigerant at the outlet of the condenser may be set at the optimum range for improving the efficiency of the cyclic operation and for assuring the cooling performance and that the favorable flow rate control characteristics which allows the refrigerant flow rate to be largely changed by the small variation of the subcooling degree may be obtained by setting the spring preset pressure within that range.
According to a seventh aspect of the present invention, the variable restrict means has a restrict passage formed into a shape such that the refrigerant having contracted at an inlet thereof adheres to an inner wall surface of the intermediate space to be decompressed by tubular friction.
Since the tubular frictional force has the relationship that it is proportional to the square of the flow velocity, it is possible to increase the opening of the variable restrict means by utilizing that the tubular frictional force increases when the flow rate is high. It also allows the action of keeping the pressure difference constant regardless of the fluctuations of flow rate to be enhanced further, thus maintaining the good refrigerant flow rate characteristics (flow rate control gain).
According to an eighth aspect of the present invention, length L2 of the restrict passage and an equivalent diameter d2 of the restrict passage satisfy a relation L2/d2xe2x89xa75.
According to the study conducted by the inventors, it was found that the operation and effect of the eighth aspect of the present invention can be obtained when the shape of the restrict passage is set so that the above-mentioned ratio becomes L2/d2 greater than 5 in concrete because the decompression effect by the tubular friction in the restrict passage is favorably exhibited.
It is noted that the equivalent diameter means that when the cross sectional shape of the restrict passage is a normal circle, the diameter of the circle is applied as it is and when it is non-circle such as ellipse, it is replaced to a circle of the equal cross sectional area and the diameter of the replaced circle is applied.
According to a ninth aspect of the present invention, it is possible to catch foreign materials within the refrigerant at the upstream side of the variable restrict means and to prevent the small passage section of the pressure reducer from clogging by the foreign materials by disposing a filter at the upstream side of the variable restrict means.
According to a tenth aspect of the present invention, the fixed valve seat is disposed at the upstream side of the valve body and the filtering is assembled in a body with the fixed valve seat.
Thus, the filter may be formed in a body with the fixed valve seat of the variable restrict means, thereby decreasing a number of parts.
According to an eleventh aspect of the present invention, the whole pressure reducer may be constructed as a thin and long cylinder by containing the variable restrict means and the fixed restrict means linearly on a same axial line within a cylindrical body member. Accordingly, the pressure reducer may be disposed readily on the way of cooling pipes even in a very small mounting space such as a vehicular engine room.
According to a twelfth aspect of the invention, a refrigeration cycle unit comprises a compressor for compressing and discharging refrigerant, a condenser for condensing the refrigerant from the compressor, a pressure reducer for decompressing the refrigerant from the condenser, an evaporator for evaporating the refrigerant which has been decompressed by the pressure reducer, and an accumulator for storing the refrigerant from the evaporator. The pressure reducer is composed of the pressure reducer described above.
The invention can exhibit the refrigerant flow rate control action effectively in such accumulator type refrigeration cycle unit.
According to a thirteenth aspect of the present invention, the compressor is driven by a vehicular engine, the condenser is disposed at the region where it is cooled by receiving running wind in running the vehicle and the evaporator cools air blown out to a car room.
Although the state (subcooling degree) of the refrigerant at the outlet of the condenser is inclined to change largely due to the fluctuations of rotational speed of the compressor, to the fluctuations of radiating capability of the condenser caused by the fluctuations of car velocity and to the fluctuations of cooling thermal load of the evaporator in the vehicular accumulator type refrigeration cycle unit, the present invention allows the refrigerant flow rate to be favorably controlled and the subcooling degree of the refrigerant at the outlet of the condenser to be maintained in the adequate range even when the operating conditions fluctuate as described above.